Ascorbic acid stain removal experience

It has taken me a while to get registered, activated, etc., but in the intervening time I have read most of your tutorials and general advice posts, especially your metals section. I have owned and maintained my own pools for 30 years and I think I have learned more from your site in the past 3 weeks about pool care and what makes the chemistry tick than in the entire previous 30 years – great sight with clear no-nonsense advice.

I have dark stains on my marcite pool surface, especially in the deep end and on the steps and underwater seats, i.e., horizontal surfaces. I have been able to remove the stains twice before with Sun Coast Iron and Cobalt stain remover, but the stains returned both times as soon as I stopped treatment. Thanks to your info on metal staining, I think I now understand why the stains come back.

Because the Iron & Cobalt remover worked so well in lifting the stains, I assumed I had iron stains. So, I have been following your ascorbic acid stain removal procedure for the past 11 days. Initial results were good, although I had an algae bloom and cloudy water for part of the time and could not see the deep end bottom, but the stains disappeared from the shallow surfaces. Over the last 4 days I have been slowly adding Cl and am just beginning to detect FC for the first time. However, the staining is back, not as bad so far, but evident. I am out of the Pink Stuff, but hopefully will get more delivered today and I will add some to see if the stains disappear again.

CuLator pack has a light blue color, which the instructions indicate is copper. The stain on the pool surface is dark grey to black, not rusty or brown colored. So I am thinking I might have been wrong about the iron and maybe I have a copper problem instead of iron.

So a couple of questions: Will the ascorbic acid lift copper stain? If it will, it doesn’t tell me it is copper, but doesn’t preclude it from being copper. I guess I could have both.

I want to do a bucket test before I proceed any further, but have delayed starting until I could start posting and asking questions as I don’t know how to interpret the tests results. I couldn’t find anything on results interpretation in your instructions, so is that something you help with?

Current analysis with Taylor K2006:
FC 0.2
CC 0.2
pH 7.3 (has been at 7.2 during the treatment period until today)
Alk 50 (normally kept at 80-110)
Ca 250
CYA 85

I’ve kept a detailed log of everything I’ve done and all test results if you want more information on what I have done. Thanks for your help,
Darrell